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Thread: Certification of Full Pressure Ram

  1. #11
    emisnug's Avatar
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    Robert Keyes
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    Quote Originally Posted by JeremyCuss View Post
    Thank you Robert. That is an excellent solution to my problem. I have rung them. They will test it next week and can do it while I wait. They will provide a certificate. What is more they only charge £40 and obviously have done quite a few rams for Robot Wars in the past!
    Great to hear! Yes, HPAC have been around for a while. Very nice bunch of guys - if Trev's there, ask him about his lawnmower tank! (I know him from tournament paintball)

  2. #12
    emisnug's Avatar
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    Hi Jeremy, did your ram get certified in the end? Trev mentioned Robot Wars parts but I didn't catch him before he went off again

  3. #13
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    No, the ram didn't get certified. The valves were pressure tested successfully up to 90 bar, but the ram leaked very badly around the seal. I am planning to replace the seal, but I haven't done so yet, because of a series of problems, which I am overcoming one at a time. I will then bring it back to HPAC for testing.

  4. #14
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    That's a shame. O ring sealing is never fun, and rarely right on the first or second try.

    What pressure are you trying to seal? I'm alright with reciprocating O Ring glands

  5. #15
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    I'm trying to seal full CO2 pressure - maybe 60barg. I'm interested in the reciprocating O ring glands that you mention. They sound like the sort of O rings used in my old 16 barg Norgren pneumatic cylinder. They were made with very soft elastomer and appeared to have a lip to seal the pressure. This old cylinder had two seals, but I only need one, as the pressure is at one side of the ram only. I have no idea where to get such seals, nor what the best material of construction would be. Any help would be appreciated.

  6. #16
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    That ram was made back in 2004.... I can imagine the oring on the piston not being all that happy with 13 years of idleness.

    Does the rod/piston move smoothly?

  7. #17
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    Quite so, Mario. There is no criticism from me of your work. I need to replace the O ring because it is old and does not allow the ram to be pressurised. I may look at other designs of O ring, which may make a better seal.

    The ram doesn't move smoothly. The problem is not the O ring seal, but the piston catching on the plastic (nylon?) seal which is inserted in the top plate of the ram. I have sanded and smoothed the ram and the plastic seal to improve the movement and will do some more to allow the ram to move freely.

  8. #18
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    The only reasons I can imagine why the nylon bushing would case "tightness" are the 2% moisture retainment and swelling it can cause or disalignment.

    In the worst case, send it back, and I'll rebuild it.
    But I cannot certify it anymore. That capacity went when I changed jobs earlier this year.

  9. #19
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    Jeremy, it sounds like you have yourself an excellent solution.

    However, if you're still interested, this here is the O Ring Bible: https://www.parker.com/literature/OR...g_Handbook.pdf

    Ingest all of that and you'll have an ok understanding of all the seals involved. Personally, I tend to run a bit more stretch on the O rings I use (a more shallow groove), but that's because I come from paintball pneumatics, where you're on the edge of a good seal and really low friction. For 60+ bar use, stick to the handbook and you shouldn't go too wrong.

  10. #20
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    I have now got a new O ring for the ram which is 5.3mm instead of 5mm diameter. The O ring fits the piston beautifully and the ram fits into the cylinder OK. It is of course much more rubbery than the old O ring. We will see how it seals. The advice the I received from the hydraulics supplier was that an O ring will probably seal better that a U ring as the ring slot in the piston was not designed for that type of seal. I will take their word for it.
    I have also sanded enough from the nylon bushing to allow the ram to travel freely. I am making progress.

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